Synthetic, spectroscopic, biological and X-ray crystallographic structuralstudies on a novel pyridine-nitrogen-bridged dimeric nickel(II) complex ofa pentadentate N3S2 ligand

The Schiff base formed by condensation of 2,6-diacetylpyridine with S-benzy ldithiocarbazate (H2SNNNS) behaves as a pentadentate ligand, forming a nick el(II) complex of empirical formula Ni(SNNNS).H2O that is high-spin with a room-temperature magnetic moment of 2.93 B.M. Spectroscopic data indicate t hat the ligand coordinates with the nickel(II) ion via the pyridine nitroge n atom, the azomethine nitrogen atom and the thiolate sulfur atom. The crys tal and molecular structure of the nickel(II) complex was determined by X-r ay crystallography. The complex crystallizes in the monoclinic system, spac e group C2/c, with a = 15.849(2), b = 18.830(2) and c = 18.447(2) Angstrom and alpha = 90 degrees, beta = 102.179(6)degrees, gamma = 90 degrees and Z = 8. The crystal structure analysis shows that the complex is dinuclear, [N i(SNNNS)](2). 2H(2)O, in which the nickel(II) ions are bridged by the two p yridine nitrogen atoms of two fully deprotonated ligands. The NiN4S2 coordi nation geometry about each nickel(II) ion can be described as a distorted o ctahedron. The Schiff base and its nickel(II) complex were tested against f our pathogenic bacteria (Bacillus subtilis, Pseudomonas aeruginosa, methici llin-resistant Staphylococcus and B. subtilis (wild type B29) and pathogeni c fungi (Saccharomyces ceciricae, Candida albicans, Candida lypolitica and Aspergillus ochraceous) to assess their antimicrobial properties. Both comp ounds exhibit mild antibacterial and antifungal activities against these or ganisms. The anticancer properties of these compounds were also evaluated a gainst Human T-lymphoblastic leukaemia cell lines. The Schiff base exhibits marked cytotoxicity against these cells, but its nickel(II) complex is ina ctive. (C) 2001 Elsevier Science B.V. All rights reserved.